All animals display some level of vigilance--watching for potential predators or parasites--as they forage.

One way of defining vigilance is by dividing an animal's time investment between heads-up (vigilant) and heads-down (foraging) effort. Vigilance can then be viewed as part of the animal's overall time budget.

Vigilance is most apparent in flocks or herds of herbivores or insectivores, such as these Canada Geese, Branta canadensis.

Note that in the pictured flock of geese, one individual is, according to the "heads-up" definition, vigilant, and the others are foraging.

Observations of vigilant behavior suggest a number of interesting questions, such as:

• How does vigilance fit into animal's time budgets?
• What factors regulate which animal(s) are vigilant at any given moment?
• How do proximity of potential predators, experience of the animals in their habitat, and the "culture" of flocks or herds affect time investment in vigilance?
• Does vigilance form part of a selfish-herd strategy, or does it better fit reciprocal altruism or kin-selection models?

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copyright ©2001 Michael D. Breed, all rights reserved